Unbiased noise test.

Started Feb 28, 2009 | Discussions thread
sidelight Senior Member • Posts: 1,013
Re: DXO

Rcihardc wrote:

Sorry but I don't believe in DXO. you tell me, how can S/N ratio in
0.1% gray be 7dB lower for 5DII vs D3X. come on 7dB!!!! this means
that the mean signal power is 10^7 times higher in D3X that is
10,000,000 times this is total BS.
What this means that Nikon performs some on chip read noise
subtraction for which they measure almost no noise for low signal
levels. FYI, this is why Nikons are not suitable for astrophotography.

Whether you believe in DxO or not, they exist. They have detailed test protocols anyone can review and critique. They have a lot of imaging expertise. Those are the results from their particular testing, same procedures used for all cameras. Are you suggesting bias in some way was introduced? If so, explain. The test basically shows the 5DII to be quite good, as are all three cameras. The lowest gray level performance shows a significant difference in this one area. I don't know how Nikon does it, but apparently it is there.

I have read Roger Clark's stuff for several years. He is great. Much is way above my head, but I tried to learn as much as I could from his work.

The Rose Criterion is just one measure of defining a cutoff S/N level. I was an analytical chemist for many years, and we would routinely use a S/N of 3 at a minimum to set a limit of detection. Some software would use S/N = 6. The noise is an average value, but there are spikes as you know, so if you want high confidence in judging real data, you must set a higher ratio. Seems like this could be applied, and is, to imaging. What is your threshold?

I agree that ultimately, I would like to see image comparisons under identical conditions to assess noise in shadow, as well as to see other image characteristics. But to me and some others at least, not all, the sensor data seems like a good starting point. DxO appears to apply their test procedures in a well controlled manner. The procedures can be discussed as to validity certainly.
--
David

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